Those are called isotopes,
the answer is 3.
each element has its own unique number of protons (atomic number) but a different number of neutrons can be shown in example number 3.
Valence électrons = are electrons in the outermost shell that is responsible for the chemical reactions of the atoms
Cross breeding plants to make better apples
Mass is calculated by using an objects inertia. Since inertia is a quality of matter that resists motion, we can apply an increasing force to an object until it accelerates.
Then, by measuring its acceleration we can now determine its mass using the simple equation F=m×a, except rewritten as m=Fa.
So we divide the force that we applied by the acceleration rate and we get the objects mass.
Without inertia this cannot be done.
∴ Answer is C
